The disclosure herein relates to the general field of systems, devices and methods for micro-and nanofabrication, including pattern transfer devices for soft lithography, contact printing, and dry transfer printing. More specifically, provided are reinforced composite stamps for printing-based assembly of semiconductor elements for the fabrication of electronic devices and systems, which provide high transfer yields and good transfer fidelity of printable semiconductor elements. In addition, processes for making and using reinforced composite stamps are disclosed.
Distributed electronic systems often require large quantities of micro-scale and/or nano-scale semiconductor structures and/or devices sparsely patterned and assembled over large area substrates. As an example, low profile heliostat concentration solar photovoltaic systems require prolific use of sparsely distributed micro-scale solar cells.
Fabrication of such distributed electronic systems predominantly relies on a two step process wherein high performance electronic circuits and solar cells are first fabricated on wafer substrates having relatively small areas. Traditionally, after completion of the circuit and/or solar cell fabrication, the semiconductor wafers are cingulated and each miniature semiconductor element or device is individually pick and placed to sparsely populate a large-area device substrate. Using conventional processing approaches, such processes become prohibitively costly and resource intensive as the number of semiconductor elements increases and their size approaches sub-millimeter dimensions.
One alternative approach for populating such distributed electronic systems is transfer printing batches of micro-scale and/or nano-scale semiconductor structures and/or devices onto device substrates using a massively parallel stamping approach. Processes related to developing a stamp-based dry transfer printing platform capable of accessing high yields, accuracy, consistency, reliability and excellent quality presents a number of challenges. These challenges arise, at least in part, from the small and hard-to-manage dimensions of the semiconductor structures and devices, as well as the properties of the stamp itself that inherently is made from fragile and miniature elements subject to flexion and other spurious properties that can hinder the ability to achieve accurate, consistent and reliable printing-based assembly.
Although composite stamps are known in the art of micro- and nanofabrication, conventional stamps for these applications suffer limitations when used for dry transfer printing of micro-scale semiconductor structures and/or devices that impede commercial development of printing-based assembly of distributed electronic systems. These limitations include, for example, short stamp life, inability to perform high-yield dry transfer printing of micro-scale semiconductor structures, unmanageable thermal contractions and mechanical deformations, lack of adaptability to nonplanar surfaces, lack of accuracy and reproducibility, uneven distribution of contact forces between the stamp printing apparatus and the top surface of a substrate being patterned, problems in efficiently attaching the stamp to a semiconductor transfer printing tool, and difficulties in transfer printing of micro-scale semiconductors on substrates having areas larger than that of the stamp.
A variety of conventional composite stamps and printing systems suffer from one or more of the above problems and limitations. Furthermore, many of those stamps and systems are designed for soft lithography on substrates which are never larger than the stamp and, therefore are not well suited for dry transfer printing to substrates having a surface area larger than the composite stamp surface area.
U.S. Pat. No. 5,512,131, issued on Apr. 30, 1996, (Kumar and Whitesides) discloses patterning systems and methods for plating self-assembled mono layers, plating and etching a surface, attaching biomolecules and forming a template from an existing pattern so as to reproduce that pattern.
U.S. Pat. No. 5,817,242 issued on Oct. 6, 1998 (Biebuyck and Michel) discloses patterning using a stamp having posts that are defined in a hard material (such as poly(methylenmethacrylate) or poly-Si) in combination with a deformable layer and a backing layer that functions as a rigid support for the stamp. Incorporation of a hard material for posts in stamps of this reference may result in limitations in the adaptability or conformability to uneven surfaces and even distribution of contact forces, thereby hindering high-fidelity patterning via dry transfer contact printing.
U.S. Pat. No. 7,117,790, issued Oct. 10, 2006, (Kendale et al.) discloses a stamp configuration incorporating a rigid glass backing that imparts a degree of reinforcement to the stamp. The glass backing of this reference, however, has a thickness that is greater than about 6 mm. Such a thick and rigid glass backplane is likely to require large pressure forces in the range of 35 to 60 kPa (5 to 8.7 PSI) to establish effective conformal contact with some substrates. Such large pressures can limit the effective lifetime of the stamp and damage fragile semiconductor structures upon transfer and assembly on substrate surfaces. The large pressures apparently required in the systems and methods of Kendale et al. may also deform the receiving substrate, limit uniformity of the printing and limit adaptability or conformability to uneven substrate surfaces. In addition, the stamp disclosed in Kendale et al. requires stiff coupling between the stamp and its actuating and sensing elements. Furthermore, to achieve co-planarity between the rigid stamp and a substrate (e.g., silicon), three coil actuators and stainless flexures are used. Due to the overall rigidity of the stamp in Kendale, it is not clear that this stamp configuration can attain a uniform pressure across the stamping area, especially in view of the excessive rigidity of the thick stamp glass backing layer. The limitations of the Kendale et al. stamps and processes are evident in the high level of printing defects shown in this reference, likely indicating that the printing pressure is non-uniform across the stamp. That stamp uses a high pressure chamber to cause the stamp backing to deflect, creating a minimum point. Such stamp backing deflection may hinder high placement accuracy due to radial distortions, especially in the case of micro-scale and/or nanoscale semiconductors elements. In addition, patterning using the system in Kendale et al. is limited to receiving substrates having an area similar in size to that of the stamp element.
U.S. Pat. No. 7,195,733, issued Mar. 27, 2007, (Rogers and Menard) discloses multilayer composite stamps for making patterns of microscale and/or nanoscale features on substrate surfaces. The composite stamps of this reference comprise a plurality of polymer layers, wherein the Young's Modulus of each layer is selected to provide patterning exhibiting good resolution and high fidelity.
As will be generally recognized from the foregoing, a need currently exists for printing-based patterning devices and processes for micro- and nanofabrication applications. Specifically, stamps capable of high performance are needed to enable a cost effective, high resolution printing-based fabrication platform for the assembly of distributed electronic devices and systems.